Method and apparatus for overcoming large transport delays between master and slave utopia devices

ABSTRACT

A system for communicating information includes a master UTOPIA device having a receive transfer controller operable to control reception of data by the master UTOPIA device and a transmit transfer controller operable to control transmission of data from the ATM switch. The system also includes a slave UTOPIA device having at least one memory area. The slave UTOPIA device includes a receive poll controller operable to determine whether the memory area is available to transmit data for receipt by the master UTOPIA device and further operable to communicate the result of the determination to the receive transfer controller. The slave UTOPIA device also includes a transmit poll controller operable to determine whether the memory area is available for receiving data to be transmitted by the master UTOPIA device and further operable to communicate the result of the determination to the transmit transfer controller.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to computer and telecommunicationsnetworks and more particularly to a method and apparatus for overcominglarge transport delays between master and slave UTOPIA devices.

BACKGROUND OF THE INVENTION

Manufacturers of network equipment encounter increasingly complex datatransfer design issues as networks and network devices have evolved intosophisticated systems. An increasing number of network systems nowutilize asynchronous transfer mode (ATM) technology, which in manyapplications provides a more effective way to transfer data across anetwork.

ATM is a layered architecture allowing multiple services like voice,data, and video to be mixed over the network. Three lower level layershave been defined to implement the features of ATM. An Adaptation Layerassures the appropriate service characteristics and divides all types ofdata into a 48 byte payload that will make up an ATM cell. An ATM Layertakes the data to be sent and adds a 5 byte header information thatassures the cell is sent to the right connection. A Physical Layerdefines the electrical characteristics in network interfaces. This layerperforms necessary operations to effect transmission of data along thetransmission media. However, ATM is not tied to a specific type ofphysical transport.

A number of protocols exist for transmission of information between theATM Layer and the Physical layer. One such protocol is the UniversalTests and Operation Physical Interface for ATM (UTOPIA) data pathinterface. UTOPIA defines the interface between the Physical Layer andupper layer modules such as the ATM Layer. The definition allows acommon physical interface in ATM sub-systems across a wide range ofspeeds and media types. UTOPIA controllers are physical devices thatimplement the UTOPIA protocol for transmitting information between thephysical layer and the ATM layer. A UTOPIA I controller is capable ofcontrolling a single slave device, a UTOPIA II controller is capable ofcontrolling a plurality of slave devices, and a UTOPIA III controller iscapable of controlling an even larger number of slave devices.

UTOPIA protocol is often used to transfer data between an ATM card and aline card. Often the DSL line card will be physically located at asignificant distance from the ATM card. Communicating data from the ATMcard to the DSL line card directly over a cable according to UTOPIAspecifications is not currently implemented because of the largetransport delays that would be associated with transmitting timingsignals and data over a large-length cable. Therefore, currentimplementations utilize two UTOPIA devices located between the ATM cardand the line card to effect such transfer.

These devices consists of a physical device located on the ATM cardacting as a UTOPIA slave and a master UTOPIA controller. Data istransferred between the ATM card and the slave physical device accordingto UTOPIA protocol, and data is transferred from the master UTOPIAcontroller to the DSL line card according to UTOPIA protocol. However,data is transferred between the slave UTOPIA physical device and themaster UTOPIA controller according to any suitable format, and typicallyin serial format.

Such an implementation for data communication between an ATM card and aphysical device, such as a DSL line card, is expensive and consumes moreresources than needed.

SUMMARY OF THE INVENTION

Accordingly, a need has arisen for a method and apparatus for overcominglarge transport delays between master and slave UTOPIA devices. Thepresent invention provides a method apparatus that addressesshortcomings of prior systems and methods.

According to one embodiment of the invention, a system for communicatinginformation includes a master UTOPIA device having a receive transfercontroller operable to control reception of data by the master UTOPIAdevice and a transmit transfer controller operable to controltransmission of data from the ATM switch. The system also includes aslave UTOPIA device having at least one memory area. The slave UTOPIAdevice includes a receive poll controller operable to determine whetherthe memory area is available to transmit data for receipt by the masterUTOPIA device and further operable to communicate the result of thedetermination to the receive transfer controller. The slave UTOPIAdevice also includes a transmit poll controller operable to determinewhether the memory area is available for receiving data to betransmitted by the master UTOPIA device and further operable tocommunicate the result of the determination to the transmit transfercontroller.

According to another embodiment of the invention, a method forcommunicating information between master and slave UTOPIA devicesincludes providing a master UTOPIA device having a receive transfercontroller operable to control reception of data by the master UTOPIAdevice and a transmit transfer controller operable to controltransmission of or from the master UTOPIA device. The method alsoincludes providing a slave UTOPIA device having a receive pollcontroller operable to determine whether the slave utopia device isavailable to transmit data and further operable to communicate theresult of the determination to the receive transfer controller and atransmit poll controller operable to determine whether the slave UTOPIAdevice is available for receiving data and further operable tocommunicate the result of determination through the transmit transfercontroller. The method further includes connecting the master UTOPIAdevice to the slave UTOPIA device and transmitting information betweenthe master UTOPIA device and the slave UTOPIA device. The step oftransmitting includes determining, by the receive poll controllerlocated on the slave UTOPIA device that the slave UTOPIA device is readyto transfer data to the master UTOPIA device, and in responseinitiating, by the receive transfer controller located on the masterUTOPIA device, transfer of data from the slave UTOPIA device to themaster UTOPIA device and determining, by the transfer poll controllerlocated on the slave UTOPIA device, that the slave UTOPIA device isready to receive data to be transmitted by the master UTOPIA device, andin response initiating, by the transmit transfer controller located onthe master UTOPIA device, transfer of data from the master UTOPIA deviceto the slave UTOPIA device.

Some embodiments of the invention provide numerous technical advantages.For example, some embodiments of the invention allow communication ofthe data between a master UTOPIA device, such as an ATM card, and aslave UTOPIA device, such as a DSL card, over a medium havingsignificant length without the adverse effects typically associated withdirect communications between the two devices. Furthermore, such datacommunication may be effected without the use of intervening UTOPIAphysical slave device and a master UTOPIA controller, thereby decreasingthe costs of implementing certain communications systems, such as DSL.According to another embodiment, the amount of memory used on the linecard is reduced because no intermediate storage is required on the linecard.

Other technical advantages are readily apparent to one skilled in theart from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionstaken in connection with the accompanying drawings in which:

FIG. 1 is a block diagram of a communications system showingconventional components utilized to transfer data between a masterUTOPIA device and a slave UTOPIA device;

FIG. 2 is a block diagram of a communications system for transferringdata from a master UTOPIA device to a slave UTOPIA device according tothe teachings of the present invention;

FIG. 3 is a block diagram of the communications system of FIG. 2 showingadditional details of the system, including ports for receiving data andinstruction signals as well as the associated signals;

FIG. 4 is a flowchart illustrating a method for receiving data at themaster UTOPIA device illustrated in FIGS. 2 and 3 from the slave UTOPIAdevice shown in FIGS. 2 and 3;

FIG. 5 is a flowchart showing method for transmitting data from themaster UTOPIA device shown in FIGS. 2 and 3 to the slave UTOPIA deviceshown in FIGS. 2 and 3; and

FIG. 6 is a block diagram showing an alternative embodiment of acommunications system for transferring data between a master UTOPIA anda slave UTOPIA device, showing additional parallel/serial converters forallowing more rapid transfer of data between the master and slavedevices.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention and its advantages are bestunderstood by referring to FIGS. 1 through 6 of the drawings, likenumerals being used for like and corresponding parts of the variousdrawings.

FIG. 1 is a block diagram of a communications system 10. Communicationssystem 10 allows communication of data between the ATM layer and thephysical layer in asynchronous transfer mode communications. Asillustrated, communications system 10 includes an ATM card 11 and a linecard 17. ATM card includes an ATM switch 12 and a physical device 14,each described in greater detail below. Line card 17 includes a DSLinterface 18 and a master UTOPIA controller 16, each described ingreater detail below. ATM switch 12 implements the functions of the ATMlayer specified by ATM specifications. These functions include adding afive-byte header that assures a cell is sent to the correct connection.Relevant ATM specifications include Utopia 3. Physical LayerSpecification af-phy0136.000, November 1999; Utopia Level 2af-phy-0039.000, June 1995; and Utopia af-phy-0017.000, March 1994, andmay be found at, for example, ATMFORUM, which is incorporated herein byreference. In this example, ATM switch 12 acts as a master UTOPIA devicebecause, as described below, it controls data transfer with it accordingto UTOPIA specifications. DSL interface 18 implements the physical layerfunctions specified by the above-referenced ATM specification. DSLinterface 18 performs necessary operations to effect transmission ofdata along a subsequent transmission media (not explicitly shown). DSLinterface 18 may be designed to implement various types of physicallayers, including DSL, Gigabit Ethernet, and SONET. In this example, DSLinterface 18 acts as a slave UTOPIA device because, as described below,data transfer with it is controlled by a master UTOPIA device.Communication with ATM switch 12 and with DSL interface 18 occursaccording to the Universal Tests and Operation Physical Interface forATM (UTOPIA). UTOPIA defines the interface between ATM switch 12 andphysical device 14 between master UTOPIA controller 16 and DSL interface18. UTOPIA includes various forms, which currently include UTOPIA I,UTOPIA II and UTOPIA III, described above.

In order to transfer data between ATM switch 12 and DSL interface 18according to UTOPIA specifications, conventional implementations utilizea physical slave device 14 and a master UTOPIA controller 16 disposedbetween ATM switch 12 and DSL interface 18. These devices 14 and 16 actas an intermediary for data transfer between ATM switch 12 and DSLinterface 18. Physical device 14 operates as a slave UTOPIA device andcommunicates with ATM switch 12 under the control of ATM switch 12, asdescribed below. Master UTOPIA controller 16 acts as a master UTOPIAcontroller and communicates with DSL interface 18 according to UTOPIAspecifications over line 24 under the control of master UTOPIAcontroller 16. Therefore, ATM switch 12 and physical device 14communicate with each other according to UTOPIA specifications, andmaster UTOPIA controller 16 and DSL interface 18 communicate with eachother according to UTOPIA specifications. Once data is transferred toeither physical slave device 14 or master UTOPIA controller 16, data maythen be transferred between device 14 and 16 over cable 22 according toany suitable format, and not necessarily UTOPIA. Cable 22 may be asuitable media for transmitting data between ATM switch 12 and line card18. One example of cable 22 is a backplane.

Transfer delays conventionally have hindered utilization of UTOPIAprotocol for transferring data over a large distance because of thetiming requirements associated with UTOPIA protocol are inconsistentwith large transport delays, which are normally associated with transferof data over a large distance. Because of this problem, physical device14 and master UTOPIA controller 16 have conventionally been used toeffect transfer between a 4 master UTOPIA device 12, such as an ATMswitch and a DSL interface 18, such as a DSL card, when the two devicesare located a large distance from each other. The invention recognizesalternative methods for directly transferring data between ATM switch 12and DSL interface 18 that do not require the superfluous use of physicaldevice 14 and master UTOPIA controller 16. Such methods may be bestdescribed by first providing a description of certain components withinATM switch 12 relevant to its operation as a UTOPIA controller.

Conventionally, ATM switch 12 includes a UTOPIA controller 28 and iscapable of controlling a slave device, such as physical slave device 14.If UTOPIA II protocol is utilized, a UTOPIA II controller located on ATMswitch 12 may control a plurality of devices 14. If UTOPIA III protocolis utilized, a UTOPIA III controller on ATM switch 12 controls aplurality of devices 14, and also allows transmission of data in 32 bits(as opposed to 16 for UTOPIA I and UTOPIA II).

UTOPIA controller 28 includes a receive UTOPIA controller 30 and atransmit UTOPIA controller 32. Receive UTOPIA controller 30 includes apoll controller 34 and a transfer controller 36. Transmit UTOPIAcontroller 32 includes a poll controller 38 and a transfer controller40. The receive poll controller 34 transmits an address 42 correspondingto a physical device from which data is to be received. In response, thephysical device, such as, in this example, physical device 14, returns acell available indication 44, to receive poll controller 34. In ananalogous manner, transmit poll controller 38 transmits an address 48corresponding to a particular physical device, such as device 14 and inresponse receives a cell available indication, as indicated by 50. Inthis manner, data is transferred from a master UTOPIA device, such asATM switch 12, to a slave UTOPIA device, such as physical device 14.

According to the teachings of the invention, poll controllers arelocated remotely from the UTOPIA controller on a UTOPIA slave device toallow communication between the UTOPIA master and the UTOPIA slavedevice, without the use of devices 14 and 16 while overcoming largetransport delays that would otherwise occur. Except where otherwiseindicated, hereinafter in this document, master UTOPIA device refers toa device that includes a transfer controller for controlling transfer ofdata with the master UTOPIA device and a slave UTOPIA device refers to adevice that is controlled in such a manner by the master UTOPIA deviceand that also includes poll controllers. This is in contrast toconventional usage that refers to master UTOPIA devices that includeboth transfer controllers and poll controllers and slave UTOPIA devicesthat do not include poll controllers. Embodiments of the invention aredescribed in greater detail in conjunction with FIGS. 2 through 6.

FIG. 2 is a block diagram illustrating a UTOPIA communications system110. UTOPIA communications system 110 includes an ATM card 111 having anATM switch and also includes a line card 114. ATM card 111 may includeother components not relevant to the present invention. ATM switch 112is one example of a master UTOPIA device, and line card 114 is oneexample of a slave UTOPIA device. Other master and slave UTOPIA devicesmay be utilized without departing from the scope of the presentinvention. ATM switch 112 and line card 114 are similar to ATM switch 12and line card 14, except as described below. ATM switch 112 communicateswith line card 114 using UTOPIA protocol over cable 122. ATM switch 112and line card 114 may communicate directly over cable 122, withoutintervening devices, such as physical slave device 14 even if cable 122has a significant length that heretofore would have prevented directcommunication between ATM switch 112 and line card 114 according toUTOPIA specifications.

According to the teachings of the invention, poll controllers 144 and146 are located on line card 114, as opposed to locating these pollcontrollers on ATM switch 112. This allows ATM switch 112 and line card114 to be located a considerable distance from each other, yetcommunicate directly. Otherwise, locating ATM switch 112 a considerabledistance from line card 114 would result in unacceptable timing delaysassociated with ATM switch 112 polling devices on line card 114.

ATM switch 112 includes a transfer controller system 128 for controllingreception of data from line card 114 and transmission of data to linecard 114. Transfer controller system 128 includes a receive transfercontroller 136 and a transmit transfer controller 140. Receive transfercontroller 136 controls reception of data by ATM switch 112. Transmittransfer controller controls transmission of data from ATM switch 112 toline card 114.

Line card 114 includes a poll control system 142 and a plurality of DSLmodems 126. Poll control system 142 controls polling of devices on linecard 114, such as a DSL modem 126. Poll control system 142 includes areceive poll controller 144 and a transmit poll controller 146. Receivepoll controller 144 controls polling of DSL modems 126 to determinewhether DSL modem 126 is prepared to transfer data from line card 114over cable 122 for receipt by ATM switch 112. Transmit poll controller146 polls DSL modem 126 to determine whether DSL modem 126 is ready toreceive data transferred by ATM switch 112. Poll controllers 144 and 146are, in one embodiment, devoid of any memory areas, resulting in lowercost implementation.

DSL modems 126 perform manipulations on data received from ATM switch 12necessary to transmit data along a digital subscriber line (DSL) and,conversely, perform manipulations on data it receives for transfer toATM switch 112. DSL modems 126 include a receive UTOPIA port assembly148 and a transmit UTOPIA port assembly 150. Receive poll controller 144communicates with receive UTOPIA port assembly 148 on DSL modems 126over bus 130. Transmit poll controller 146 communicates with transmitUTOPIA port assembly 150 on DSL modems 126 over bus 132. Additionaldetails of UTOPIA communications system 110 and its operation aredescribed in conjunction with FIG. 3.

FIG. 3 is a block diagram of communication system 110 showing additionaldetails of the system. As illustrated, receive transfer controller 136includes a plurality of ports associated with communication according toUTOPIA protocol. Those ports are identified below according toconventional UTOPIA name and by reference numeral. The ports include astart of cell port 152 (SOC), a data port 154, a return clock port 156(RTCLK), a clock signal port 158 (CLK); an address port 60 (ADDR), apoll enable port 162 (POLL ENABLE), a serial cell available port 164(SERIAL CLAV), and a start of serial cell available port 166 (SOCLAV).These ports receive and transmit information as described below.

Start of cell port 152 receives an indication that data is about to betransmitted. Data port 154 receives data transferred from line card 114.Return clock port 156 receives a clock signal returned from pollcontroller 144 that aligns incoming data. Clock port 158 provides aclock signal to DSL modem 126 to control timing of transfer of data fromDSL modem 126 to ATM switch 112. Address port 160 provides the addressof a particular DSL modem 126 that will provide data for receipt by ATMswitch 112. Poll enable port 162 provides an indication that polling ofDSL modems 126 should begin or stop. Serial cell available port 164receives serial cell available information for each DSL modem 126. Startof serial cell available port 166 receives an indication from receivepoll controller 144 that serial cell available information transmittedto port 164 is about to be initiated.

Transmit transfer controller 140 includes the same type of ports asreceive transfer controller 136, as identified here: a start of cellport 168, a data port 170, a return clock port 172, a clock signal port174, an address port 176, a poll enable port 178, a serial cellavailable port 180, and a start of cell available port 182. The ports ontransmit transfer controller 140 function in a similar manner as thoseon receive transfer controller 136 with the following differences: startof cell port 168 and data port 170 provide, rather than receive,respective signals, as compared to receive transfer controller 136.

Receive poll controller 144 on line card 114 also includes a number ofports for receiving and transmitting information. Those ports areidentified here as: a poll enable port 184 (POLL ENABLE), a serial cellavailable port 186 (SERIAL CLAV), a start of serial cell available port188 (SOCLAV), a cell available port 190 (CLAV), an address port 192(ADDR), a clock port 193 (CLK), and a return clock port 194 (RTNCLK).

Transmit poll controller 146 includes the same types of ports and areidentified as follows: a poll enable port 196, a serial cell availableport 198, a start of serial cell available port 200, a cell availableport 202, a clockport 203, an address port 204, and a return clock port206.

Poll enable port 184 on receive poll controller 144 receives anindication from receive transfer controller 136 that polling shouldbegin. Serial cell available port 186 provides serial cell availableinformation for each of DSL modems 126 to receive transfer controller136. Start of cell available port 188 provides to receive transfercontroller 136 an indication that serial cell available port 186 isabout to transfer serial cell available information for DSL modems 126.Cell available port 190 receives an indication from DSL modem 126 thatit is available to receive data. Address port 192 provides an addresslocation identifying a particular one of the devices 148 from which datawill be received by ATM switch 12. Address port 192 also receives anaddress from address port 160, which may be used to verify that aparticular one of devices 148 is ready to transfer data. Clock port 193receives a clock signal from transfer controller 136. Return clock port194 provides a return clock signal to receive transfer controller 136 tocontrol timing of reception of data by ATM switch 112 from line card114.

The ports on transmit port controller 146, described above, provide orreceive analogous information as the respective ports describe above inconjunction with receive poll controller 144.

As illustrated, each of DSL modems 126 includes a receive port assembly148 and a transmit port assembly 150. Receive port assembly 148 operatesto provide data for receipt by ATM switch 112 under the control ofreceive transfer controller 136 on ATM switch 112. Transmit portassembly 150 operates to receive data transmitted by ATM switch 112under the control of transmit transfer controller 140. The portsassociated with each port assembly are described below.

Receive port assembly 148 includes a start of cell port 210 (SOC), adata port 212 (DATA), a cell available port 214 (CLAV), a clock port 216(CLK), and an address port 218 (ADDR). Start of cell port 210 providesan indication that data is about to be transmitted to receive transfercontroller 136 on ATM switch 112. Data port 212 provides data fortransfer from receive port assembly 148 to ATM switch 12 through receivetransfer controller 136. Cell available port 214 provides an indicationto receive poll controller 144 that device 126 is prepared to transmitdata for receipt by ATM switch 112. Clock port 216 receives a clocksignal to control timing of polls and resulting signaling and datatransfer. Address port 218 receives the address of the particular DSLmodem 126 that will provide the data for receipt by ATM switch 112.

Transmit port assembly 150 includes similar ports with the followingdifferences: A start of cell port 230 and a data port 232 each receivetheir respective signals rather than provide their respective signals,as is the case with analogous ports on receive port assembly 148.

As described above, communications system 110 operates to allowcommunication of data between ATM switch 112 and UTOPIA devices such asmodems. Accordingly, two modes of operation exist. In a receive mode,ATM switch 112 receives data from DSL modems 126. In a transmit mode,ATM switch 112 transmits data from ATM switch 112 to DSL modems 126.Each of these modes is described separately below in conjunction withFIGS. 4 and 5.

FIG. 4 is a flowchart illustrating a method for receiving data at ATMswitch 112 that is transferred by line card 114. The method begins atstep 300. At a step 302 receive transfer controller 136 expresses adesire to have DSL modems 126 polled to determine whether a particulardevice is ready to transmit data for receipt by ATM switch 112. To doso, receive transfer controller 136 outputs from poll enable port 162 asignal 259 for receipt by poll enable port 184 on receive pollcontroller 144. Signal 259 is set to “1,” indicating polling shouldbegin. At a step 304, receive poll controller 144 polls all DSL modems126 and accumulates cell available signals 280 provided by cellavailable ports 214 of receive port assembly 148. In response, at step306 receive poll controller 144 outputs from serial cell available port186 a signal 260 that includes a serialized version of the cellavailable status for each DSL modem 126. Signal 260 therefore providesto receive transfer controller 136 at serial cell available port 164 anindication of which devices are available to transmit data for receiptby ATM switch 12.

As part of step 306 of transmitting the serial cell availableinformation from receive poll controller 144 to receive transfercontroller 136, a start of serial cell available signal 262 is providedfrom start of cell available port 188 to start of cell available port166 along signal 262. Signal 262 therefore provides an indication that aserial cell available signal 260 is about to be transmitted.

At step 308, when receive transfer controller 136 receives on serialcell available port 164 signal 260 indicating that a DSL modem 126 isavailable to transmit data for reception by ATM switch 112, receivetransfer controller 136 transmits from poll enable port 162 a pollenable signal 259 having a value of “0.” Such a signal received byreceive poll controller 144 at poll enable port 184 halts polling of DSLmodems 126. This allows subsequent transfer of cells.

At step 310 receive transfer controller 136 initiates data transfer forreception by ATM switch 112 by outputting the address of a selectedavailable DSL modem 126 that is ready to transfer data. This step isperformed by outputting signal 258 for receipt by address port 218 onreceive port assembly 148. Clock signal 256, which is provided by clockport 158, controls timing of transfer of data between line card 114 andATM switch 112.

In response to step 310, receive port assembly 148 associated with thespecified address signal 258 transmits data according to UTOPIAspecifications at step 312. In this regard, start of cell port 210 onreceive port assembly 148 outputs signal 250 for receipt by start ofcell port 152 on receive transfer controller 128. Signal 250 indicatesthe beginning of a data transfer. A data port 212 on receive portassembly 148 also transmit data as data signal 252 for receipt by dataport 154 on receive transfer controller 136, thereby effecting datatransfer from line card 114 to ATM switch 112. Return clock port 194outputs a return clock signal 254 for receipt by return clock port 156for aligning receipt of data signal 252 and clock signal 256. Returnclock signal 254 is generated based on clock 256 and is returned toreturn clock port 156 to control timing of data receipt. Delayassociated by generating return clock signal 254 at return clock port194 on line card 114 data signal 252, which originated from line card114, may be appropriately aligned by return clock signal 254. Oncetransmission begins, the method continues with step 302 in which asignal 259 is reset to 1 to enable continued polling of all devices 126.This polling may occur while data are transferred.

In the above-described manner, data is transferred from a UTOPIA device,such as line card 114 and received by ATM switch 112. According to theteachings of the invention, such transfer may occur over a significantlength cable 122 while overcoming significant transport delay.

FIG. 5 is a flowchart illustrating a method of ATM switch 112transferring data to DSL modems 126. Many of the steps associated withtransferring data to DSL modems are analogous to the corresponding stepsassociated with receiving data at ATM switch 112. The method begins atstep 400. At a step 402, transmit transfer controller 140 on ATM switch112 output on poll enable port 178 signal 274 equal to “1.” Signal 274is received by poll enable port 196 on transmit poll controller 146.Setting signal 274 equal to “1” instructs transmit poll controller 146to poll all devices 126. At a step 404, transmit poll controller 146polls all physical devices. In doing so, transmit poll controller 146receives cell available signals 282 from cell available ports 234.Signal 282 indicates, for each device 126, whether the device isavailable to receive data transmitted by ATM switch 112.

Transmit poll controller 146 receives the cell available information andconverts it into a serial cell available signal, which is transmitted atserial cell available port 198 for receipt at serial cell available port180 on transmit transfer controller 140. Transmit poll controller 146additionally provides at start of cell available port 200 an indicationthat the serial cell available signal 276 is about to begin. Signal 278is received by transfer controller 140 at start of cell available port182. If signal 276 indicates that the device to which data is to betransferred is available, polling is halted by transmit transfercontroller 140 transmitting from poll enable port 178 a signal 274 equalto “0.” Such a value for signal 274, which is received by poll enableport 196 on transfer poll controller 146, halts polling by transmit pollcontroller 146. If signal 276 indicates the device 126 to which data isto be transferred is not available, polling continues (not explicitlyshown).

After polling by transmit poll controller is halted, transmit transfercontroller outputs an address of device 126 to which data is to be senton address port 176. Also transmitted by transmit transfer controller140 is a clock signal 270 provided at clock port 174 and the data to betransferred provided at data port 170. The data signal 266, clock signal270, and address signal 272 are received by respective ports on transmitport assembly 150 on the device 126 associated with the addressindicated by signal 272.

After data transfer is initiated, transmit transfer controller 140transmits from poll enable port 178 signal 274 equal to “1” to continuepolling at step 402.

In the above-described manner, data is transferred from ATM switch 112and received by a UTOPIA device, such as line card 114. According to theteachings of the invention, such transfer may occur over a significantlink cable 122 while overcoming significant transport delay.

FIG. 6 is a block diagram of an alternative embodiment of acommunications system 410 according to the teachings of the presentinvention. Communications system 410 is substantially similar tocommunications 110, except that a parallel/serial converter 416 isincluded within line card 414 and a parallel/serial converter 418 isincluded within ATM card 411. Any suitable parallel/serial converter maybe used and preferably high speed converters are used. An exampleconverter is a Low Voltage Differential Signa (LVDS) converter. In allother respects, ATM card 411 and line card 414 are similar to ATM switch111 and line card 114, respectively. By utilizing converters 412 and416, the above-described data transmitted over cable 122 may betransmitted in a faster manner by converting the parallel data to serialform for transfer over cable 122 and then converting back to parallelform for use within ATM card 411 and line card 414 as described above.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made therein without departing from the spirit andscope of the present invention as defined by the appended claims.

1. A system for communicating information comprising: a master UTOPIAdevice comprising: a receive transfer controller operable to controlreception of data by the master UTOPIA device; and a transmit transfercontroller operable to control transmission of data from an ATM switch;a slave UTOPIA device comprising at least one memory area, the slaveUTOPIA device comprising: a receive poll controller operable todetermine whether the memory area is available to transmit data forreceipt by the master UTOPIA device and further operable to communicatethe result of the determination to the receive transfer controller,wherein the receive poll controller includes a port selected from agroup consisting of a roll enable port, a serial cell available port, astart of serial cell available port, a cell available port, an addressport, a clock port, and a return clock port; and a transmit pollcontroller operable to determine whether the memory area is availablefor receiving data to be transmitted by the master UTOPIA device andfurther operable to communicate the result of the determination to thetransmit transfer controller.
 2. The system of claim 1, wherein themaster UTOPIA device comprises an ATM card.
 3. The system of claim 1,wherein the slave UTOPIA device comprises a DSL line card.
 4. The systemof claim 1, wherein the master UTOPIA device comprises an ATM card andwherein the slave UTOPIA device comprises a DSL line card, and furthercomprising a backplane directly connecting the ATM card to the DSL linecard.
 5. The system of claim 1, wherein the receive poll controller andtransmit poll controller are each operable to transmit a return clocksignal to an ATM card the ATM card for aligning data transferred to orreceived from the ATM card.
 6. The system of claim 1, wherein thereceive poll controller and the transmit poll controller are devoid ofany memory areas.
 7. The system of claim 1, wherein the port comprises apoll enable port.
 8. The system of claim 1, wherein the port comprises aserial cell available port.
 9. The system of claim 1, wherein the portcomprises a start of serial cell available port.
 10. The system of claim1, wherein the port comprises a cell available port.
 11. The system ofclaim 1, wherein the port comprises an address port.
 12. The system ofclaim 1, wherein the port comprises a clock port.
 13. The system ofclaim 1, wherein the port comprises a return clock port.
 14. A UTOPIAslave device comprising: a receive poll controller operable to determinewhether a memory location on the UTOPIA slave device is available totransmit data for reception by a UTOPIA master device, wherein thereceive poll controller includes a port selected from a group consistingof a poll enable port, a serial cell available port, a start of serialcell available port, a cell available port, an address port, a clockport, and a return clock port; and a transmit poll controller operableto determine whether a memory location on the UTOPIA slave device isavailable to receive data to be transmitted by an ATM device.
 15. Thedevice of claim 14, wherein the receive poll controller includes a pollenable port, a serial cell available port, a start of serial cellavailable port, a cell available port, an address port, a clock port,and a return clock port.
 16. The device of claim 14, wherein thetransmit poll controller includes a poll enable port, a serial cellavailable port, a start of serial cell available port, a cell availableport, an address port, a clock port and a return clock port.
 17. Thedevice of claim 14, wherein the UTOPIA slave device comprises aplurality of DSL modems.
 18. The device of claim 14, and furthercomprising a serial/parallel converter for converting data received bythe UTOPIA slave device into parallel format and for converting datatransmitted by the UTOPIA slave device to serial format.
 19. The deviceof claim 14, wherein the receive poll controller is operable to poll aplurality of DSL modems for determining whether each modem is availableto transfer data.
 20. The device of claim 14, wherein the transmit pollcontroller is operable to poll a plurality of DSL modems to determinewhether the DSL modem is ready to receive data.
 21. A UTOPIA masterdevice comprising: a receive transfer controller operable to communicatewith a receive poll controller located remote from the UTOPIA masterdevice on a UTOPIA slave device and further operable to controlreception of data by the UTOPIA master device from the UTOPIA slavedevice, wherein the receive transfer controller comprises a portselected from a group consisting of a start of cell port, a data port, areturn clock port, a clock port, an address port, a poll enable port, aserial cell available port, and a start of cell available port; and atransmit transfer controller operable to communicate with a transmitpoll controller located remote from the UTOPIA master device on theUTOPIA slave device and further operable to control transmission of databy the UTOPIA master device to the UTOPIA slave device.
 22. The deviceof claim 21, wherein the receive transfer controller comprises a startof cell port, a data port, a return clock port, a clock port, an addressport, a poll enable port, a serial cell available port, and a start ofcell available port.
 23. The device of claim 21, wherein the transmittransfer controller comprises a start of cell port, a data port, areturn clock port, a clock port, an address port, a poll enable port, aserial cell available port, and a start of cell available port.
 24. Thedevice of claim 21, wherein the receive transfer controller is operableto produce a poll enable signal specifying to the receive pollcontroller locator remote from the UTOPIA master device that polling ofa plurality of transferring devices should begin.
 25. The device ofclaim 21, wherein the transmit transfer controller is operable totransmit a poll enable signal to the transmit poll controller, for apoll enable signal specifying that a plurality of modems should bepolled to determine which device is prepared to receive data.
 26. Thedevice of claim 21, wherein the receive transfer controller and thetransmit transfer controller are each operable to produce respectivepoll enable clock signals for transmission, respectively, to the receivepoll controller and the transmit poll controller and further operable toreceive, respectively, from the receive poll controller and the transmitpoll controller a return clock signal for aligning data, respectively,received or transferred to the master device.
 27. A method forcommunicating information between master and slave UTOPIA devicescomprising: providing a master UTOPIA device having a receive transfercontroller operable to control reception of data by the master UTOPIAdevice and a transmit transfer controller operable to controltransmission of or from the master UTOPIA device; providing a slaveUTOPIA device having a receive poll controller operable to determinewhether the slave UTOPIA device is available to transmit data andfurther operable to communicate the result of the determination to thereceive transfer controller and a transmit poll controller operable todetermine whether the slave UTOPIA device is available for receivingdata and further operable to communicate the result of determinationthrough the transmit transfer controller, the receive poll controllercomprising a port enable port; connecting the master UTOPIA device tothe slave UTOPIA device; receiving, at the port enable port of the slaveUTOPIA device from the master UTOPIA device, a poll enable signal to theslave UTOPIA device, the poll enable signal indicating a request for theslave UTOPIA device to poll a plurality of physical devices to determinewhether any one of the physical devices is available to receive data;and transmitting information between the master UTOPIA device and theslave UTOPIA device, wherein said transmitting comprises: determining,by the receive poll controller located on the slave UTOPIA device thatthe slave UTOPIA device is ready to transfer data to the master UTOPIAdevice, and in response initiating, by the receive transfer controllerlocated on the master UTOPIA device, transfer of data from the slaveUTOPIA device to the master UTOPIA device; and determining, by thetransfer poll controller located on the slave UTOPIA device, that theslave UTOPIA device is ready to receive data to be transmitted by themaster UTOPIA device, and in response initiating, by the transmittransfer controller located on the master UTOPIA device, transfer ofdata from the master UTOPIA device to the slave UTOPIA device.
 28. Themethod of claim 27, wherein determining, by the receive poll controller,that the slave UTOPIA device is ready to transfer data to the masterUTOPIA device comprises receiving a poll enable signal at the receivepoll controller from the receive transfer controller.
 29. The method ofclaim 28, wherein determining, by the receive poll controller, that theslave UTOPIA device is ready to transfer data to the master UTOPIAdevice further comprises polling a plurality of modems on the UTOPIAslave device determine whether each modem is available to transfer data.30. The method of claim 27, and further comprising transmitting by themaster UTOPIA device a poll enable signal to the slave UTOPIA device,the poll enable signal indicating that the slave UTOPIA device shouldpoll a plurality of modems to determine whether they are ready totransfer data.
 31. The method of claim 27, and further comprisingtransmitting by the master UTOPIA device a poll enable signal to theslave UTOPIA device, the poll enable signal indicating that the slaveUTOPIA device should poll a plurality of modems to determine whetherthey are ready to receive data.
 32. The method of claim 27, and furthercomprising receiving at the master UTOPIA device, a return clocks signalor aligning data to be received by the master UTOPIA device from theslave UTOPIA device.
 33. The method of claim 27, and further comprisingtransmitting a poll enable signal from the master UTOPIA device to theslave UTOPIA device, the poll enable signal indicating that the slaveUTOPIA device should halt polling of modems.
 34. A system forcommunicating data between a master UTOPIA device and a slave UTOPIAdevice comprising: a transmit control means for controlling transmissionof data from the master UTOPIA device to the slave UTOPIA device; areceive control means for controlling reception of data at the masterUTOPIA device from the slave UTOPIA device; a transmit poll means fordetermining whether the slave UTOPIA device is ready to receive datatransmitted by the master UTOPIA device and for communicating the resultof said determination to the transmit control means; a receive pollmeans for determining whether the slave UTOPIA device is ready totransmit data for reception by the master UTOPIA device and forcommunicating the result of said determination to the receive controlmeans; a cable means disposed between and connecting together the masterUTOPIA device and a slave UTOPIA device; and wherein the transmitcontrol means and receive control means are separated from the transmitpoll means and the receive poll means by the cable means.